This invention relates to a liquid metal mechanical pump having a hydrostatic bearing immersed in liquid, and more specifically to an improved liquid metal mechanical pump to reduce thermal shocks to a bearing of the pump by providing a partition wall around the bearing.
The most common design of a mechanical pump for liquid metal is a vertical, free liquid level type centrifugal pump which has a liquid metal contained in a casing and a cover gas sealed over the liquid level. This type of mechanical pump employs a hydrostatic bearing immersed in the liquid to rotatably support the lower end of a drive shaft of the pump and is constructed such that a part of the liquid forced out of a diffuser is supplied by the delivery pressure of the pump to the hydrostatic bearing to lubricate it by the liquid metal itself. In a conventional prior art pump of this type, one example of which is shown in FIG. 1, the liquid coming out of the diffuser 14 is directly supplied to the hydrostatic bearing 20. (Common reference numerals are assigned to the component parts of FIG. 1 that are identical to those of the embodiments of the present invention hereinafter described, and their construction and action will become apparent during the course of the following explanations.)
Thus, when operated under a thermal transient condition, the hydrostatic bearing 20 is subjected to the thermal shocks bringing about deterioration of the mechanical strength of the bearing material and making it difficult to maintain the function of the bearing due to the fact that the clearance between a bearing sleeve 5 and a bearing bush 6 is usually 0.4 to 0.5 mm. With the conventional pumps these problems still remain to be solved. To describe in more detail, the main loop pump for a liquid metal-cooled fast breeder reactor is subject to various thermal transient conditions in the event of fault or when the normal operating condition has been changed. Especially with the primary loop pump installed in the hot leg arrangement of the reactor, it is reported that the cold shock which the pump would undergo under the scram thermal transient condition has a temperature gradient of 3.degree. C./sec, a temperature variation range of 150.degree. C. and an expected frequency of 500 times (during the design life of 30 years). It should also be noted that the rated operating temperature is more than 500.degree. C. It is therefore understood that reduction in thermal shocks to the bearing and in creep constitutes the major consideration in manufacturing the hot leg pump. On the other hand, the primary loop pump of cold leg arrangement also has problems such as the cold shock to the bearing at the time of the scram thermal transient condition and the hot shock caused when the secondary loop pump is tripped.